Which habitats will thrive or die in acidifying oceans?

Dissolved carbon dioxide is expected to be a scourge on our oceans – but there is hope for marine diversity. Evelyn Fetterplace reports.

A scorpionfish lurking in a seagrass meadow in the Mediterranean Sea. New modelling suggests seagrass will thrive as the oceans acidify.

Wolfgang Poelzer / Getty Images

Our oceans are acidifying as carbon dioxide levels rise, and some marine habitats will wither away. But it’s not all bad news – others such as seagrass meadows will flourish, new research suggests.

Whether the species that live within them will too is another story.

Jennifer Sunday from the University of British Columbia in Canada and a team of international researchers investigated how changing ocean chemistry affected coral reefs, mussel beds, seagrass meadows and seaweed habitats.

In Nature Climate Change, they found some habitats could grow perfectly well in acidified water, and might provide refuge for their resident species.

Ocean acidification – caused by dissolved carbon dioxide in seawater making carbonic acid – spells doom for many marine species by making it difficult for them to grow and reproduce.

When these species live in a habitat that’s also harmed by acidification, this damage is accelerated.

Coral reefs, in particular, are at risk. Their calcium carbonate structures are eaten away by the extra carbonic acid.

To see how other habitats might fare as the pH drops, Sunday and her crew modelled habitat health based on existing biodiversity data.

Not surprisingly, organisms that rely on calcium structures, including coral, did not enjoy acidification.

But seagrass meadows showed the opposite. They use carbon dioxide to photosynthesise and more dissolved gas means more energy for them.

The density of most, but not all, seagrass habitats in the study increased under their modelling, so the researchers predicted the diversity of species that live within them might be safeguarded.

But there’s not yet any clear evidence that seagrass is the oceans’ saviour. The direct effects of acidification on species are easy to see. But figuring out how a whole ecosystem will react is far more difficult – and will need a whole lot more exploration, the researchers write.